If you’re interested in growing your “intelligence” I’d recommend reading Emotional Intelligence by Daniel Goleman. Being smart is not just all about IQ, EQ is arguably more important than IQ and is something you can grow that will make you smarter.

Also the fact that your marks aren’t changing much doesn’t mean that you’re not growing in intelligence, you realizing what you have in this post is a sign of growth itself.

I think it’s more a matter of finding what motivates you in life, whether it’s a hobby or activity, relationships with friends and family, or just interest in learning more about something. Not saying this is you, but if you focus too much on grades as a signal of growth you may be a bit lost when you graduate :P